I use JPA->Hibernate. PlayFramework. I want to have relationship.
Category - 1:n -> Tag
Every category can have many tags, but tags do not know about it.
So, i do like this:
#Entity
public class Category ... {
#OneToMany
public List<Tag> tags = new LinkedList<Tag>();
}
I have test:
#Test
public void playWithTags() {
Tag tag1 = new Tag("tag1").save(); // managed by playframework
Category cat1 = new Category("cat1");
cat1.tags.add(tag1);
cat1.save();
// check if tag1 and cat1 were saved
assertEquals(1, Tag.count());
assertEquals(1, Category.count());
Category cat2 = new Category("cat2");
cat2.tags.add(tag1);
cat2.save();
}
The result is:
16:18:01,555 ERROR ~ Duplicate entry '1' for key 'tags_id'
16:18:01,555 ERROR ~ Could not synchronize database state with session
org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelp
....
java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.sql.BatchUpdateException: Duplicate entry '1' for key 'tags_id'
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2020)
It seems that cat2.save() try to do more then it should
If if use merge() instead of save() it works good:
cat2.merge();
BUT WHY?
I have fixed the problem. The problem was in that, that I used NOT THAT annotation. So i just changed #OneToMany to #ManyToMany and voilà - No any restrictions anymore.
But if saying about the OneToMany then it seems there was a unique-restriction on database-level which prevented us to put not-unique values to tags_id. Therefore we could not put same tag to One category. I.e. it wanted One category for Many tags, but if tags were already 'used' - no way.. I tried to put unique=true/false in #JoinTable -> #JoinColumn - but it does not help. For me it's still strange, but at least current problem was fixed.
You're mixing up two concepts: Primary key and foreign key.
There can be only one PK but FK just means "there must be an element with this ID in some other table". FK doesn't constrain uniqueness.
[EDIT] Your problem is that you're mixing entities. How did you get the tag1 which is returned by save()?
This entity must be one which you get from Hibernate, not the result from new. Even if it looks insane, you must do this in save():
session.save(tag);
return session.load(tag.getId());
This way, you get an entity that is managed by Hibernate. Only when the entity is managed by Hibernate, Hibernate knows when it has to save the entity and when it has already been saved.
So when you do cat2.tags.add(tag1); in your example above, Hibernate thinks "oh, I don't know anything about this tag, it must be a new one".
And tries to save the tag again.
Related
In a legacy project we had issues where if a developer would forget a project_id in the query condition, rows for all projects would be shown - instead of the single project they are meant to see. For example for "Comments":
comments [id, project_id, message ]
If you forget to filter by project_id you would see all projects. This is caught by tests, sometimes not, but I would rather do a prevention - the dev should see straightaway "WRONG/Empty"!
To get around this, the product manager is insisting on separate tables for comments, like this:
project1_comments [id,message]
project2_comments [id,message]
Here if you forgot the project/table name, if something were to still pass tests and got deployed, you would get nothing or an error.
However the difficulty is then with associated tables. Example "Files" linked to "Comments":
files [ id, comment_id, path ]
3, 1, files/foo/bar
project1_comments
id | message
1 | Hello World
project2_comments
id | message
1 | Bye World
This then turns into a database per project, which seems overkill.
Another possibility, how to add a Behaviour on the Comments model to ensure any find/select query does include the foreign key, eg - project_id?
Many thanks in advance.
In a legacy project we had issues where if a developer would forget a project_id in the query condition
CakePHP generates the join conditions based upon associations you define for the tables. They are automatic when you use contains and it's unlikely a developer would make such a mistake with CakePHP.
To get around this, the product manager is insisting on separate tables for comments, like this:
Don't do it. Seems like a really bad idea to me.
Another possibility, how to add a Behaviour on the Comments model to ensure any find/select query does include the foreign key, eg - project_id?
The easiest solution is to just forbid all direct queries on the Comments table.
class Comments extends Table {
public function find($type = 'all', $options = [])
{
throw new \Cake\Network\Exception\ForbiddenException('Comments can not be used directly');
}
}
Afterwards only Comments read via an association will be allowed (associations always have valid join conditions), but think twice before doing this as I don't see any benefits in such a restriction.
You can't easily restrict direct queries on Comments to only those that contain a product_id in the where clause. The problem is that where clauses are an expression tree, and you'd have to traverse the tree and check all different kinds of expressions. It's a pain.
What I would do is restrict Comments so that product_id has to be passed as an option to the finder.
$records = $Comments->find('all', ['product_id'=>$product_id])->all();
What the above does is pass $product_id as an option to the default findAll method of the table. We can than override that methods and force product_id as a required option for all direct comment queries.
public function findAll(Query $query, array $options)
{
$product_id = Hash::get($options, 'product_id');
if (!$product_id) {
throw new ForbiddenException('product_id is required');
}
return $query->where(['product_id' => $product_id]);
}
I don't see an easy way to do the above via a behavior, because the where clause contains only expressions by the time the behavior is executed.
I have a problem retrieving values of a column from relations in Laravel.
I have a User - Model. This model has relation to a table btw. a model named Userhobbies.
For now we have:
User ::: hasMany >>> Userhobbies
Now with User::all()->load('hobbies') I'm getting right results like
{"id":"1","username":"jdoe","first_name":"Joe","last_name":"Doe","birth":"
1992-04-11","picture_id":"f3dca65323e876026b409b9ba3d49c56","hobbies":
[{"hobby_id":"1","user_id":"1"},{"hobby_id":"2","user_id":"1"},
{"hobby_id":"3","user_id":"1"},{"hobby_id":"4","user_id":"1"}]}
As you can see Userhobbies contains only primary-key relations between hobby - table (Hobby Model) and user - table (User Model).
(Hobby model also has hasMany relation to Userhobbies)
My question now is - how to retrieve all hobby-names (from hobby - table) in my call over (after load('hobbies') ) and is it possible without writting a lot of code?
For better understanding of my idea the result which I want to retrieve:
{"id":"1","username":"jdoe","first_name":"Joe","last_name":"Doe","birth":"
1992-04-11","picture_id":"f3dca65323e876026b409b9ba3d49c56","hobbies":
["golf", "cards", "games", "football"]}
EDIT:
If I try following (I tried with belongsToMany in User and Hobby):
User::with('hobbies')->get()->first()
And I'm getting the whole values from the hobbies - table:
{user-specific data ...
hobbies:[{"id":"1","name":"golf","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"1"}},
{"id":"2","name":"cards","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"2"}},
{"id":"3","name":"games","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"3"}},
{"id":"4","name":"football","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"4"}}]}
Same try with ->load('hobbies'). I really don't know how to go on.
To explain it a bit more what I need one could imagine such query as follows:
User::all(['id', 'name'])->load(array('hobbies.id','hobbies.name'))->get();
From my knowledge, I know that it's possible to use a closure to set constraints on the query that performs the load, like so:
User::all()->load(['hobbies' => function($query)
{
$query->select('id', 'name');
}]);
By doing it, when you cast it to array, it will produce a result near to what you want. You can even add 'pivot' to your $hidden property on your Hobby model to hide this information.
The structure of concerning tables is as follows (MySQL):
//Table Name : team
tid PK
team_name (varchar)
//Table Name : fixture
fid PK
home_team_id FK |_ both referenced to 'tid' from 'team' table
away_team_id FK |
My aim is to retrieve the team names. Considering this structure, I think I'll have to retrieve home_team_id and away_team_id and then do something like
Fixture::where('tid','=',$home_team_id)->get();
My question is, is this the correct way to accomplish what I aim to do?
and
should this be done from the controller? (if so, then I'll have to do two queries from same function)
First, rather than having your primary keys be tid and fid, just keep them both as id. This is not only best practice, but will allow you to more easily use Laravel's Eloquent ORM as it by default assumes your primary key column is named id.
Second thing, make sure your table names are in plural form. Although this is not necessary, the example I'm about to give is using Laravel defaults, and Laravel assumes they are in plural form.
Anyway, once you've 'Laravelized' your database, you can use an Eloquent model to setup awesome relationships with very minimal work. Here's what I think you'd want to do.
app/models/Team.php
class Team extends Eloquent {
// Yes, this can be empty. It just needs to be declared.
}
app/models/Fixture.php
class Fixture extends Eloquent {
public function homeTeam()
{
return $this->belongsTo('Team', 'home_team_id');
}
public function awayTeam()
{
return $this->belongsTo('Team', 'away_team_id');
}
}
Above, we created a simple model Team which Laravel will automatically look for in the teams database table.
Second, we created model Fixture which again, Laravel will use the fixtures table for. In this model, we specified two relationships. The belongsTo relationship takes two parameters, what model it is related to, in both cases here they are teams, and what the column name is.
Laravel will automatically take the value in away_team_id and search it against the id column in your teams table.
With just this minimal amount of code, you can then do things like this.
$fixture = Fixture::find(1); // Retrieves the fixture with and id of 1.
$awayTeam = $fixture->awayTeam()->first(); // var_dump this to see what you get.
$homeTeam = $fixutre->homeTeam()->first();
Then you can proceed as normal and access the column names for the tables. So say you have a 'name' column in the teams table. You can echo out the the home team name from the fixture like so.
$fixture = Fixture::find(1); // Get the fixture.
echo $fixture->homeTeam->name;
It's nearly 2AM, so there might be an error or two above, but it should work.
Make sure you check the docs for Eloquent, especially the bits relating to relationships. Remember to name your columns and tables in the way Laravel wants you to. If you don't, there are ways to specify your custom names.
If you want to get even more fancy, you can define the inverse relationship like this on your Team model.
app/models/Team.php
class Team extends Eloquent {
public function fixturesAtHome()
{
return $this->hasMany('Fixture', 'home_team_id');
}
public function fixturesAway()
{
return $this->hasMany('Fixture', 'away_team_id');
}
}
Then to get all of a particular team's home fixtures...
$team = Team::find(1); // Retreive team with id of 1;
$homeFixtures = $team->fixturesAtHome();
in an app i have an entity that contains a list of other entities (let's say an event holding a list of assigned employees)
using objectify - i need to find all the events a particular employee is assigned to.
is there a basic way to filter a query if it contains the parameter - kind of the opposite of the query in
... quick pseudocode
findAll(Employee employee) {
...
return ofy.query(Event.class).filter("employees.contains", employee).list();
}
any help would be greatly appreciated
i tried just doing filter("employees", employee) after seeing this http://groups.google.com/group/objectify-appengine/browse_thread/thread/77ba676192c08e20 - but unfortunately this returns me an empty list
currently i'm doing something really inefficient - going through each event, iterating through the employees and adding them to a new list if it contains the given employee just to have something that works - i know this is not right though
let me add one thing,
the above query is not actually what it is, i was just using that because i did not think this would make a difference.
The Employee and Events are in the same entity group with Business as a parent
the actual query i am using is the following
ofy.query(Event.class).ancestor(businessKey).filter("employees", employee).list();
unfortunately this is still returning an empty list - does having the ancestor(key) in there mess up the filter?
solution, the employees field was not indexed correctly.
I added the datastore-indexes file to create a composite index, but was testing originally on a value that I added before the employees field was indexed, this was something stupid i was doing - simply having an index on the "business" field and the "employees" field fixed everything. the datastore-indexes file did not appear to be necessary, after deleting it and trying again everything worked fine.
Generally, you do this one of two ways:
Put a property of Set<Key<Employee>> on the Event
or
Put a property of Set<Key<Event>> on the Employee
You could also create a relationship entity, but if you're just doing filtering on values with relatively low counts, usually it's easier to just put the set property on one entity or the other.
Then filter as you describe:
ofy.query(Event.class).filter("employees", employee).list()
or
ofy.query(Employee.class).filter("events", event).list()
The list property should hold a Keys to the target entity. If you pass in an entity to the filter() method, Objectify will understand that you want to filter by the key instead.
Example :
/***************************************************/
#Entity
#Cache
public class News {
#Id Long id;
String news ;
#Index List<Long> friend_list = new ArrayList<Long>();
// My friends who can see my news , exemele : friend_list.add(id_f1); friend_list.add(id_f2); friend_list.add(id_f3);
//To make an operation on "friend_list", it is obligatory to index it
}
/*************************************************/
public News(Long id_f){
List<Long> friend_id = new ArrayList<Long>();
friend_id.add(id_f);
Query<Nesw> query = ofy().load().type(News.class).filter("friend_list in",friend_id).limit(limit);
//To filter a list, just after the name of the field you want to filter, add "IN".
//here ==> .filter("friend_list in",friend_id);
// if friend_list contains "id_friend" ==> the query return value
.........
}
I have a Model called Version that looks like this:
from google.appengine.ext import db
import piece
class Version(db.Model):
"A particular version of a piece of writing."
parent_piece = db.ReferenceProperty(piece.Piece, collection_name='versions')
"The Piece to which this version belongs."
note = db.TextProperty()
"A note from the Author about this version."
content = db.TextProperty()
"The actual content of this version of the Piece."
published_on = db.DateProperty(auto_now_add=True)
"The date on which the version was published."
I would like to access instances of Version via their IDs, using Version.get_by_id(), but this call always returns None. I can see in the Datastore Viewer that they have ID values, and in the debugger, I can query for them but not use them:
>>> for each_ver in version.Version.all():
... print each_ver.key().id()
...
34
35
36
31
32
>>> a = version.Version.get_by_id(34)
>>> type(a)
<type 'NoneType'>
I see that there are plenty of questions here where people are able to use get_by_id() effectively just as I wish, and they do not see the results that I am seeing.
Could the problem be that each Version instance is a child in an Entity Group rather than a root of an Entity Group? Each Version lives in an Entity Group that looks like Member->Piece->Version. If that is the problem, is there a way that I can refer to Version entity without using its entire key? If that is not the problem, can anyone tell me what I can do to make get_by_id() work as expected?
Could the problem be that each Version
instance is a child in an Entity Group
rather than a root of an Entity Group?
Yes. An entity's key includes the keys of any parent entities.
If that is the problem, is there a
way that I can refer to Version entity
without using its entire key?
No. An entity is uniquely identified only by its entire key, which includes the keys of all the parent entities. If you know the kinds of its parent entities, though, you can use db.Key.from_path to construct the key from the chain of IDs or key names.
I had your same problem but in ndb.Model and I found that I need to convert the ID to an int. So maybe using version.Version.get_by_id(int(34)) can solve your problem.